This project is investigating the nature of humoral antibodies which prevent induction of delayed hypersensitivity to purified antigens in mice, and the mechanisms by which they are effective. These antibodies appear to interfere with antigen-cell interaction which should result in sensitization. Their effects on tissue and cellular distribution of sensitizing antigen in skin and lymph nodes will be investigated using an enzyme antigen that reveals its own presence. The antibodies may function by having particular cell affinities, either alone or in combination with antigen and perhaps other serum constituents. Such affinities will be investigated. The antibodies probably are made in a burst of manufacture, soon after boosting, by B-type lymphocytes. The distribution and identity of these cells will be studied. Although research to date indicates with high probability of correctness that the inhibitory antibodies belong to an anodic subclass of mouse IgF proteins, more experimentation toward increasing the certainty of their identification will be done, especially using the help of enzyme antigen as a very sensitive indicator of antibody activity among serum proteins. BIBLIOGRAPHIC REFERENCES: Crowle, A. J.: Theoretical considerations of immunodiffusion analyses useful in clinical chemistry. Clin. Chem., 1976. Yonemasu, K., and Crowle, A. J.: Guinea pig contrasensitizing antibodies effective in mice. Proc. Soc. Exp. Biol. Med., 1976.